How to adjust the AE or otherwise apply custom exposure settings?

[uap-remi]

I've been trying to speed up image acquisition on my current allsky camera build. But after having virtually tried out everything, I somehow managed to corrupt libcamera or something within. So now, with a fresh OS install I want to approach things differently.

My issue is that the current auto exposure algorithm choses settings that degrade the image quality (particularly too high ISO). I've already come up with a simple low ISO algorithm and would like to use it. But in any case, as others have already pointed out, turning off AE doesn't really work well. I tried using a custom tuning file but it's either not found or something within causes an out of range error. Also setting the controls using set_controls() is sometimes being overwritten by default settings.

With capturing to raw buffer streams, things even get more inconsistent. I somehow managed to get the Pi to cycle through insane exposure settings, going from under- to overexposure. Primarily I just want to lock the ISO to 200. Only achieved that with capturing raw buffers and converting/saving them to files but that results in the above cycling behavior.

In any case I'm kinda running out of ideas. Does anyone have advice? Anybody else here trying to get proper manual mode to work? Just to be clear. Using already existing allsky software is not an option since they are (as far as I know) using libcamera/raspistill terminal commands. Am considering INDI again but it's too much overhead. My 3b+ doesn't have enough RAM to properly run it and building from source takes a day. Not good.

Cheers.

[davidplowman]

Hi, I think the most obvious thing I would try would be to change the exposure profiles. For the IMX477, you can find them here (Pi 4 or earlier), or here (Pi 5).

You will probably find them on your system in /usr/share/libcamera/ipa/rpi/vc4 (Pi 4 or earlier) or /usr/share/libcamera/ipa/rpi/pisp (Pi 5). You can edit them in situ, but you'll have to be root, and take a backup first just in case!

Tip: I often start by putting a syntax error into the tuning file (e.g. insert an 'x' as the first character in the file) and checking that the camera fails to start. This confirms you're editing the right file. (I have spent far too long editing the wrong tuning files and wondering why it wasn't working like I expected...)

Although there are separate tuning files, the exposure profiles work the same on all platforms. Something like

                                "shutter": [ 100, 1000000 ],
                                "gain": [ 1.0, 12.0 ]

should ramp the exposure time up to 1s while keeping the analogue gain at 1x, after which the analogue gain will ramp to 12x with the exposure time fixed at 1s.